A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic of the text. It gives a broad overview of what a tropical cyclone is. It does not refer to any previous information. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'The weakest tropical cyclones...' which uses 'the', making it dependent on prior context. Paragraph 3 starts with 'If a depression intensifies...' which is conditional and needs more context. Paragraph 4 starts with 'Once a tropical cyclone reaches...' which also needs context. All these reasons make them not independent.

Concluding sentence: Why this is the last line? This paragraph is the last line because it concludes the discussion about tropical cyclones. It gives the final classification of the strongest type of cyclone, which is a hurricane. This follows the Conclusive Words rule.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the topic of tropical cyclones. It gives a specific example of the weakest type of tropical cyclone. This follows the Broader to Specific Strategy.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains what happens when a tropical depression gets stronger. It shows a logical order of events from a weak cyclone to a stronger one. This follows the Logical Order rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it continues the idea of intensifying cyclones. It explains what happens when the storm gets even stronger. This follows the Cause and Effect Relationship rule.